The present invention relates to an electrical desiredvalue transmitter, particularly for an electronic gas-pedal system in general.
More particularly, the invention relates to an electrical desired-value transmitter, particularly for an electronic gas-pedal system which has a return spring (5), a force elastic jump spring (15) with play arranged parallel thereto, and an electrical path converter which is connected to both springs and gives off a desired-value signal, as well as a safety contact.
Such desired-value transmitters are used in so-called electric gas systems which are developed as follow-up control in order to transmit the position of a gas pedal to a throttle vale or some other element which affects the fuel/air mixture of an internal combustion mixture and is arranged in the vicinity of the combustion engine. For this purpose, the desired-value transmitter, which has an electric path converter, gives off an electric desired-value signal to an electronic regulator in which the desired-value signal is compared with a position feedback signal of the throttle valve. Since the electric gas system is subject to the same safety requirements as a purely mechanical transmission of the position of the gas pedal to the throttle valve by rods or a Bowden cable, it is constructed in accordance with strict criteria of reliability and safety. In order to assure the necessary inherent reliability of the electric gas system, as in the case of a short circuit, a safety contact is provided on the desired-value transmitter which is actuated by the gas pedal and is also known as a pedal contact. This pedal contact is opened in the idling position of the gas pedal and closed upon depressing the pedal after a given path has been exceeded. The pedal contact is arranged in an electrical circuit which furthermore contains a setting-member contact which is connected to the throttle valve as well as a fuel pump relay or a switch which acts on the ignition for reducing the output of the internal combustion engine. The pedal contact and the setting-member contact are so developed and arranged in the manner of an OR gate that only in the case of a disturbance are both contacts opened and, as a result, the gasoline pump turned off via the fuel pump relay or the ignition.
Another safety requirement for electric gas systems is that in case of a break of the return spring which moves the gas pedal automatically into the idle position when it is released, the output of the internal combustion engine be reduced. In order to satisfy this safety requirement, it is state of the art to provide, in addition to the return spring, a second return spring in parallel thereto, so that in the event that one of the two return springs breaks at least a weak return force is still definitely available. The second return spring, however, results in a more complicated construction of the desired-value transmitter. This problem is further intensified if the principle of the redundant return spring is utilized in known desired-value transmitters, which, in addition to the return spring, have at least one force elastic jump spring arranged in parallel with the inclusion of play. The force elastic jump spring produces an additional restoring force when the gas pedal has been depressed a distance which corresponds at least to the play. When the principle of redundant springs is employed, a second force elastic jump spring is also necessary, which further complicates the construction of the desired-value transmitter.